Purification of crude aromatic hydrocarbons



Patented Sept. 24, 192 91 a UNITED STATES PATENT OFFICE ALPHONS O. JAE-GER, OF GRAFTON, PENNSYLVANIA, ASSIGNOR TO THE SELDEN COM- IPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF DELANARE PURIFICATION or CRUDE AROMATIC HYDROCARBONS Np Drawingf Original application filed April 12, 1926, Serial No. 101,561. filed October 11, 1927. Serial No. 225,601.

This invention relates to the purification of V crude aromatic hydrocarbons, and more par ticularly, to the purification of light d1st1llates from coal and oil tar and light 011s con- 5 densed from coal gas. a Crude coal or oil tar distillates are usually washed with dilute acid and'with alkali to remove bases and acid compoundssuchas phenols, followed by' repeated washlng w th small amounts of concentrated sulfuric acld. This process is open to many objections. In the first place, while 'sulfurlc acid-removes some unsaturated compounds falrly well, many acyclic compounds such as paraifins l and CS besides other sulfur compounds,

alicyclic compounds and heterocyclic com-- pounds such as thiophenes are not removed or are only partially removed. The'resulting commercial hydrocarbons such as com- !0 mercial benzene, toluene, xylene, solvent naptha, etc., are not suiiiciently pure for many "purposes. It is possible to obtain highly purified hydrocarbons by the use of a sufficiently large 5 amount of sulfuric acid and oleum but the lossesof hydrocarbons are so high as to render the process commercially impracticable. A further drawbacklies in the fact that the I sludge which contains acid resins and other 0 impurities is frequently considerably decomposed by the acid and is therefore of little or no'value.

In my co-pending application, Serial No. 86,099, filed February 4, 1926, I have de- 5 scribed and claimed a method of purify ng crude aromatic hydrocarbons by selective halogenation whereby the impurities are changed into compounds having boiling points for'the most part considerably above 0 that'of aromatic hydrocarbons and in the ease of carbon disulfide into carbon tetrachloride which is harmless for most purposes bwing to its great chemical inertness. I have also described the use of various halogen car- 5/riers, such as iodine, bromine, sulfur 'compounds, metal chlorides, compounds of antimony and the l ike. In this applicatiom I have further described the I production of sludges which consist in large part of halogen 0 bodies and can be used as a; raw material for x Divided and this application the like, the present invention produces sludges of as high quality as those described 1n my co-pending application, above referred to, and from which sludges many valuable products, such as solvents, light colored resins, such as cumaron and indene resins, and the like are produced. In addition, the sulfuric acid wash may actually increase the effectiveness of the halogenation treatment. A further advantage consists in the fact that it is possible to remove certain undesirable and worthless products by means of sulfuric acid so that when the partially purified distillatf is treated with halogen, the resulting 7 halo enated products which are later sep arated by distillation are free from the unde sired products which have been removed by the sulfuric acid and are accordingly more suited'to commercial utilization and cons'ti so tute more valuable products. The sequence of treatments with acid and halogen according to the present invention can be-most varied. 'Thus,the distillates can be freed from phenols and bases by treatment with alkali and dilute acid and then given one or more washes withgconcentra'ted sulfuric acid fdllowed by treatment with halogen. In certain other cases, it may be desirable to treat first withhalogen and then wash with acid.- This may be desirable where certain easily attacked impurities are desired in the form of halogenated or halogen treated products.

Halogenation may be employed immediately after the removal of bases from the distillates by the dilute acid and" in such cases, excellent aromatic hydrocarbons can be obtained after the distillation and the impurities, particularlyin the case of benzols, from a valuable mixture which can be used as a solvent or for other purposes. The aromatic hydrocarbons, of course, are free from many of the impurities which are not removed by ordinary sulfuric acid wash and also are free from carbon disulfide which has been transformed into carbon tetrachloride or other harmless products.

When the halogen treatment is preceded by one or more concentrated sulfuric acid Washes, some unsaturated compounds are first attacked and removed, and as has been pointed out above, the impurities which are removed after halogenation are not contaminated with some of the unsaturated products and are thus a more homogeneous and more useful product which is particularly desirable when the product is to be used as a solvent. The aromatic hydrocarbon fractions which are obtained are entirely similar to those obtained by the halo en treatment without sulfuric acid wash, an of course, are

characterized by the same high grade of purity and substantial absence of impurities which interfere with (their use in catalytic reactions. I

The preliminary treatment with the sulfuric acid is particularly desirable in the case of heavier distillates such as solvent naptha and the like as these distillates contain not only resin forming bodies like cumaron and indene, but .also other unsaturated alifatic compounds whichare non-resin forming and which are easily attacked by sulfuric acid. These products are removed by the acid wash and the following haloge'nating process removes the last traces of alifatic compounds or-undesirable alicyclic compounds such as cyclopentadiene and dicyclopentadiene. Heterocyclic compounds, such as the thiophenes are also removed together with styrol and toa certain'extent hydrindene which are transformed into high boiling halogenated products. Thesolvent naptha or heavy solvent fractions' are removed by distillation and the reduction or elimination of sulfuric acid washing prevents undesired polymerization of the cumarons and indenes present. The solvent naptha thus provisionally purified can be subjected to conditions which favor polymerization and the ,resinophores polymerize to form high grade resins of very 'light color. The aromatic hydrocarbons can be distilled off and are obtained in a high state of purity; The yields of resins and aromatic hydrocarbons are very high.

By combining the sulfuric acid wash process with the halogenationproc esg'it is possible to remove the undesired impurities in precisely the form in whichthey best can be used. Thus, certain impurities which are desired in a polymerized form can be removed by sulfuric acid, whereas other products which are desired in' the form of halogenated bodies can be removed by the halogenating treatment. The combined process removes in harmless products.

oil fractions can be purified by removing alifatic hydrocarbons such as pentane, hexane, amylene, hexylene, 'heptylene, octylene,

- alicyclic compounds suchvas 'cyclopentadiene,

dicyclopentadine, diand tetrahydrobenzene, hyd-rindene and the like, heterocyclic com-- pounds such as pyrrol, pyridine, thiophene, thiotolene, thioxene, and the like. Other sulfur compounds particularly carbon disulfide' which may be present in'the' crude fractions are attacked by halogen and are transformed into other compoundssuch as carbon tetrachloride in the case of carbon disulfide. The presence of carbon tetrachloride in aromatic iydrocarbons is practically harmless as this compound is so indifferent that it does not interfere with the use of the hydrocarbons in catalytic processes or forthekproduction of intermediates to be used in catalytic processes particularly reductions and hydrogenationsr The aromatichydrocarbons roduced by;

the present process are thus pr ctically free from'sulfur and are in a state of high purity. The halogenat ion of the partially washed orude'distillates or condensates may be effect ed by chlorine, or by bromine, but I have found that iodine is notactive and accordingly the expression active halo en which will be' usedhereafter in the speci cation and claims is intended to include chlorine and bromine, but to exclude'iodine. It should be noted, however, that iodine is an excellent halogen carrier, particularly'for the halogenation of carbon disulfide. The halogenation may be effected by the use of elementar halogensuch as chlorine, gaseous or liqui or bromine or solutions such as chlorine or bromine water, bodies yielding chlorine or bromine, such as 'aqu-aregia, phosgene, sulfuryl chloride, nitrosyl chloride, hypochlor- 'ite's, hypobromites, chlorides or hydrochloric acid in the presence of oxidizers and the like.

Sulphur or sulfur compoundssuch as sulfur halides, sulfuryl chloride, thionylchloride, benzene sulfochloride and homolog'ues, are preferably used single or together as halogen carriers as they preferentially catalyze the halogenation and particularly the chlohalides of antimony, tin, gold,- tellurium, zirconium, uranium, vanadium, bismuth, molybjdenum, z1nc, copper, and nlckel compounds, animal charcoal, wood charcoal-or any other ,well known halogen carriers. 7 The reaction may also be advantageously .carried out in the presence of light, heat-or silent electric discharge. Combinations of the chemical mixtures enumerated above and thephysical catalysts such as light, heat and the like may entially catalyze the halogenation of the sevnum turnings, ferric chloride, iron scale, iron,

sesquioxide, iron sulfide, ferrous carbonate, ferrous sulfate, antimony, either in the form of powdered metal, oxide or chloride. Chemical compounds of the catalysts which prefereral classes of impurities may also be used.

The carriers may be added before or during halogenation or may be formed in halogenation, for example, sulfurylchloride which acts as chlorinating agent and carrier at the same time. Other combinations are also possible.

Unremoved sulfuric acid andhydrochloric acid formed during chlorination may be neutralized by adding suitable substances before, during or after chlorination. Examples of neutralizing substances are soda ash, caustic alkalics, lime, slaked and unslaked, calcium carbonate, magnesia, ammonia and similar substances. I f

The purification by halogenation may be carried out in anhydrous vapor phase by adding suitable driers such as anhydrous calcium chloride or copper sulfate, quick lime, etc.

becarried out in the presence of steam or water. In most cases the action of steam or water is to dilute the chlorine or chlorinating agent and there is also a strong tendency to prevent undesired condensation or polymerization. This latter feature may be of considerabl importance where large amounts of resinifiable substances are present, as in crude solvent benzene and it is desired to prevent or retard condensation. The use of water or steam in vapor phasapurification also aids in Washing the distillate if allowed to con-' dense with it or in the case of higher boiling hydrocarbons a i more complete separation may be brought'about by maintaining the condenser above theboiling point of water. In vapor phase purifications the steam may be introduced wholly into, the :liquid phase or into the vapor' phaseor partly in one and partly in tlieot-her; Chlorine and steam may I be introduced together or separately. The

steam may be wet er superheated and may be at about the boiling temperature of the mixture or may be at a much higher temperature and serve partly or. wholly as the heating means.

The sequence of treatment with acid and withhalogen, the numbers andinten'sities of treatments, of-course', will vary with the products treated and with the use of which the impuritiesare to be put. I have outlined The halogenation in vapor phase, may also certain general principles guiding the choice of procedure and these principles will be further illustrated in the specific examples. The

invention is, however, not limited to the details therein set forth and in any particular case, the skilled chemist will be guided in his choice ofprocedure by the conditions of the particular distillate or condensate with which he is Working.

Ewamp-Ze 1 I A low boiling crude benzene fraction coritaining 23% of toluene and the usual im- I purities is freed from phenols and bases in the usual manner by means 'of alkali and sulfuric acid. The product is then treated with O2 to 0.5% by volume of 66 B. sulfuric acid with vigorous agitation. The agitation is continued for 10-15 minutes, care being taken that the. oil does not become too Warm. The mixture is then allowed to settle and the tar acid which settles out in about 10 minutes is drawn off. After another 10 minutes, a further portion of the acid willhave settled out and is also drawn ofi, whereupon the oil is washed with cold or warm water. The product is distilled in a column and gaseous chlorine is introduced into the bottom of the column, the rate of introduction being regulated so that the distillate after washing, gives no color with the standard sulfuric acid test. The distillate can be collected and washed with water or dilute alkali or the vapor may be condensed in a Wash tower or the hydrochloric acid formed may be removed in any other suitable manner. The process can be made a continuous one by adding fresh amounts of crude ben zene to the still and removing the chlorinated impurities from the bottom of the still through a drain pipe. The chlorinated toluene may be recovered from the waste sludge when it is present insufficient amount to' warrant recovery. The other components of thesludge may also be utilized as described in the examples above. A yield of highly purified benzcnefrom 97 to 99% of the theory is obtainable and is not only substantially free from sulfurcompounds but is also relatively free from toluene.

Example 2 ly catalyzes the chlorination of the impuria ties and permits ac'onsiderable increase in outputfrom the same apparatus. The sulfuryl chloride boils at a relatively high temperature and tends to flow back into the still Where it is removed with the waste sludge;

Small amountsof unreacted sulfur dioxide may at times pass off into the d1st1llate but can be readily removed with an alkaline wash.

E sample 3 A low boiling crude benzene fraction is purified as described in Examples 1 and 2. The still column is filled with iron fragments as a catalyst. 'The purification is very rapid but care should be taken not to use more chlorine than that required to combine with the impurities and with the toluene, as in the presence of sufficient chlorine iron catalyzes the chlorination of benzene itself.

In the claims, the expression, coal tar distillate, is used to cover not only true distillates from coal tar, but also mixtures of the like.

. matic hydrocarbons which comprises subjecting an aromatic hydrocarbon mixture cymtainmg acyclic, ahcychc and heterocychc 1mpurities to the action of an amount of strong 30/ partially purifiedmixture to selective halosulfuric acid insuflicient to purify the mixture to a commercial product of the customary purity and thereupon subjecting the genation with an amount of active halogen suflicient to react, with substantially all of the impurities but insuflicient to effect substantial nuclear halogenation of thearomatic hydrocarbons, the selective halogenation taking place in the vapor phase.

2. The method of producing purified-aromatic hydrocarbonswhich comprises subjecting an aromatic hydrocarbon mixture Eontaining acyclic, alicyclic and heterocyclic impurities to the action of an amount of strong sulfuric acid -insuflicient to purify the mixture to a commercial product vof the customary purity and thereupon subjecting the partially purified mixture to selective halogenation with an amount of active halogen sufiicient to react with substantially all of the impurities but insufiicient to effect substantial nuclear halogenation of the'aromatic hydrocarbons,'the selective halogenation taking place in the vapor phase by means of gaseous halogen in .the presence of a solidhalogen carrier. j

3. The method of producing purified aro matic hydrocarbons which comprises subjecting an aromatic hydrocarbon mixture containing acyclic, alicyclic and heterocycl'ic impurities to the action of an amount of strong sulfuric acid insufiicient to purify the of steam.

\ mixture to a commercial product of the customary purity and thereupon subjecting the partially purified mixture to selective halogenation with an amount of active halogen suflicient to react with substantially all of the impurities but insufficient to effect substantail nuclear halogenation of the aromatic hydrocarbons, the selective halogenation being carried out in the vapor phase under condi tions and in the presence of re-agents which favor side chainhalogenation. k i a 4. The method of preparing purified bydrocarbons which comprises distilling a mixture of aromatic hydrocarbons containing acyclic, alicyclic and heterocyclic impurities which has been subjected to treatment with an amount of strong sulfuric acid insuflicient to purify the mixture to a commercial product of the customary purity, passing the vapors through a reflux column, introducing gaseous active halogenating agents into the column in amount sufiicient to react with-the impurities in the vapor but insufi icient to effect substantially nuclear halogenation of the aromatic hydrocarbons, the halogen reacted impurities of high boiling pointbeing permitted to flow back into the still-and bemg continuously removed therefrom.

5. The process according to claim 4 in which gaseous active halogenating agent is diluted with substantially inert-gaseous material.

6. The methodof producing purified aro- .matic hydrocarbons which comprises subjecting anaromatic hydrocarbon mixture containing acyclic, alicycle and heterocyclic impurities to the action of an amount 'of strong sulfuric acid insuflicient to purify the mixture to a commercial product of the cus-' tomary purity and thereupon subjecting the partially purified mixture to selective halogenation with an amount of active halogen sufficient to react with substantially all the impurities but insuificient to efi'ect substantial nuclea r halogenation of the aromatic hydrocarbons, the selective halogenation tak- 1ng-place 1n the vapor phase in the presence 7. The method of producing purified aro- -matic hydrocarbons which comprises subjecting an aromatic hydrocarbon mixture impurities to the action of an amount of strong sulfuric acid insufiicient to purify the mixture to a commercial product of the customary purity and thereupon subjecting'the partially purlfied mixture to selective halogenation with an amount of active halogen sufficient to react with substantially all of the impurities but insuflicientto effect substantial'nuclear halogenatiouof the aromatic hydrocarbons, the selective halogenation taking place in both vapor and liquid phase,

. 8. The process according to claim 4 in which the selective halogenation takes place containing acyclicgalicyclic and heterocyclic 

